The gonadotropins, follicle stimulating hormone (FSH), luteinizing hormone (LH), and chorionic gonadotropin (CG) are required for ovulation, spermatogenesis, and the biosynthesis of sex steroids. A single hypothalamic hormone, gonadotropin-releasing hormone (GnRH, also known as luteinizing hormone-releasing hormone, LHRH) is responsible for regulating the secretion of both FSH and LH in mammals. LHRH has the structure EQU 5-OxoPro--His Trp--Ser--Tyr--Gly--Leu--Arg--Pro--GlyNH.sub.2
In recent years considerable research effort has been expended on finding synthetic analogs of LHRH having equal or greater potency. These efforts have produced a number of LHRH agonists and antagonists. Attention has been particularly focused on modification of various positions to effect greater potency and in positions 5 and 6 to reduce the tendency of these LHRH analogs to stimulate histamine release.